Huma Abedin, Hillary Clinton’s aide, is interviewed by House panel on Benghazi

Huma Abedin, former Secretary of State Hillary Rodham Clinton’s closest and longest-serving aide, underwent more than five hours of questioning Thursday by the House Select Committee on Benghazi that lawmakers described as a productive interview.

Mrs. Abedin’s closed-door session with investigators on Capitol Hill served as a prelude to Mrs. Clinton’s public testimony next week before the committee, which is probing the events surrounding the 2012 terror attack on a U.S. diplomatic compound in Benghazi, Libya, that killed Ambassador J. Christopher Stevens and three other Americans.

Mrs. Abedin, who has been at Mrs. Clinton side as her personal assistant — or “body woman” — since the 2008 presidential race and currently services as a top official on Mrs. Clinton’s presidential campaign, knows as much as anyone about what goes on in Clinton World.

The interview began at 10 a.m., with Mrs. Abedin bracing for questions about the terror attack and her boss’ unusual email setup at the State Department that now is the subject of a separate FBI investigation.

Mrs. Clinton’s email only came up in questioning pertaining to the Benghazi attack, said Rep. Lynn Westmoreland, Georgia Republican and a member of the Benghazi committee.

“If it wasn’t about Benghazi, it wasn’t a question,” he told reporters outside the meeting room.

Mrs. Abedin, the wife to former Rep. Anthony Weimer who resigned in 2011 over a sexting scandal, did not answer questions as she walked through the throng of reporters outside the meeting room during several breaks in the interview.

Earlier, another Republican lawmaker on the committee described Ms. Abedin as cooperative and said she provided information, thought he declined to discuss details of her testimony.

“Mrs. Abedin conducted herself in a very professional manner, with all the questions deeply connected to the mission of our committee,” said Rep. Mike Pompeo, Kansas Republican.

Mr. Pompeo pushed back against accusations by Mrs. Clinton and her Democratic allies that the committee is a partisan political witch hunt designed to undermine her presidential campaign, including claims that it was unnecessary to call Mrs. Abedin to testify.

He said Mrs. Abedin was called because “she was a senior official in the State Department at all the relevant times and so was privy to and had access to information pertaining to all the things surrounding events in Benghazi.”

The Obama administration and Mrs. Clinton, who was secretary of state at the time, has been criticized for lax security at the compound and for a slow response to the attack, as well as statements afterwards inaccurately attributing the attack to a spontaneous riot in response to an anti-Islam YouTube video mocked Islam’s Prophet Muhammad.

Mrs. Abedin close working and personal relationship with Mrs. Clinton has made her a key figure in the email scandal, including recent revelations that she apparently had access to her boss’ account at the State Department.

She’s also come under scrutiny for pocketing a $33,000 payout from the State Department for unused leave and using her simultaneous employment inside and outside of government to cater to the Clintons’ friends and associates.

Mrs. Abedin remained tight lipped, brushing past reporters during occasion breaks from the interview.

Earlier, Rep. Elijah E. Cummings, Maryland Democrat and ranking member of the committee, told reporters that the evidence was irrefutable that the investigation was a taxpayer-financed political hit job.

He added that there was no reason for Mrs. Abedin to have been called in for an interview, with the committee’s Republican leaders informing the press when and where it would take place.

“These people most closely associated with Mrs. Clinton seem to be treated differently,” he said.

Mr. Cummings, who attended the first 90 minutes of the Abedin interview, said Mrs. Clinton’s former chief of staff, Cheryl Mills, and Mrs. Clinton’s close confidant Sidney Blumenthal, received the same treatment.

He said the House Majority Leader Kevin McCarthy, California Republican, and Rep. Richard Hanna, New York Republican, had admitted that the committee’s purpose is to injure Mrs. Clinton’s presidential run.

Mr. McCarthy in a TV interview two weeks ago boasted that the committee caused Mrs. Clinton’s poll numbers to drop.

In the course of the investigation, it was revealed that Mrs. Clinton exclusively used a private email account for official business as secretary of state and had not turned over her official correspondence to the government for nearly two years after leaving office. But committee members insist the mission remains to probe the terror attack and find out how to better safeguard U.S. diplomatic teams in the future.

Still, the ensuing scandal and Mrs. Clinton’s evolving explanations for the unusual email setup, including her use of a private email server located to her New York home, contributed to a rapid drop in the polls.

Mr. McCarthy’s comment fueled Democratic attacks on the committee and helped derail Mr. McCarthy’s bid to be the next speaker of the House.

Mr. Hanna also characterized the Benghazi committee as a partisan operation in a radio interviewWednesday, saying of Mr. McCarthy’s comment, “Sometimes the biggest sin you can commit in D.C. is to tell the truth.”

Mr. Cummings said the real question facing the Benghazi committee is about Mr. McCarthy and Mr. Hanna. “Are they telling the truth?” he asked.

Mr. Pomeo said that Democratic lawmakers never wanted the committee to succeed.

“Throughout this entire time, they have not lifted a single finger to help us uncover the facts surrounding the deaths of these four Americans,” he said. “They haven’t asked for a document, they haven’t sought a witness and they have not in good faith participated in these efforts.”